Process for the production of ketene and acetic anhydride



June 9, 1964 E. s. PAINTER ETAL 3,136,811

PROCESS FOR THE PRODUCTION OF KETENE AND ACETIC ANHYDRIDE Filed May 24, 1960 2 Sheets-Sheet 1 TO cons/v35:

I /2ms2R U A BURNER DA MPE R STACK Edwin SPaintel' Robert G. Petreg John H. JensenJn IN V EN TORS' /QLJM A-FEED-IN B FEED-IN NIf M ATTORNEYS June 1964 E. s. PAINTER ETAL 3,136,811

PROCESS FOR THE PRODUCTION OF KETENE AND ACETIC ANHYDRIDE Filed May 24. 1960 2 Sheet s-Sheet 2 CIEREHEAT A HAMBER 43 E (KING ncmcxms STREAM-A 45 f A WZEQ A CHAMBER 41 CHAMBER STREAM-B B 1] f B 46 Fli .3

- CONDENSER DENSITROL 63 mvo can 6! AIR-OPERATED VALVE 67 FOR HoAc FEED CRUDE HEAT 66 PRODUCT EXCHANGER Edwin/S. Painter R obert 0'. P9 trey J ohnHJensenJz I NV EN TORS' XMM Md M M ATTORNE YS 3,136,811 PROCESS FQR TI E PRODUCTHGN OF KETENE AND ACETIC ANHYDRIDE Edwin S. Painter, Robert C. Petrey, and John H. Jensen, Jn, Kingsport, Tenn, assignors to Eastman Kodak Compan Rochester, N.Y., a corporation of New Jersey Filed May 24, 1960, Ser. No. 31,441 3 Claims. (Cl. 260-546) This inventionrelates to the manufacture of ketenes and anhydrides. More particularly, this invention concerns the manufacture of ketene by the pyrolysis of acetic acid and the conversion of the ketene to acetic anhydride.

The manufacture of ketenes and anhydrides by the pyrolysis of various compounds such as acids, ltetones and other ketenizable materials is practiced on a large scale in the industry. A number of patents and publications describe processes and apparatus pertaining to such subject matter.

For example, our co-workers Patents 2,258,985 and 2,393,778 describe one and two chamber furnaces and processes for the pyrolysis of various ketenizable organic compounds. A three chamber furnace is described in US. Patent 2,541,471. In Painter Patent 2,784,065 (one of the inventors herein) another embodiment of a three chamber furnace is disclosed. Such prior processes and apparatus are quite efficient and produce satisfactory pyrolysis products. However, it is apparent from the economic standpoint that the development of process and apparatus whereby the yields of ketene and the like products from pyrolysis may be increased and more uniform products obtained represents a highly desirable result.

After extended investigation we have found a process and apparatus arrangement whereby the yield of ketene may be increased, costs of operation reduced and other advantages obtained as will be described in detail hereinafter. i

This invention has for one object to provide a more efiicient process for the manufacture of ketenes. A particular object is to provide an improved procedure for the pyrolysis of acetic acid to ketene. Another object is to provide a better way of converting ketene to acetic anhydride whereby more uniform results may be secured.

A special object is to provide a new arrangement whereby the over-all yield of ketene may be increased. Still another object is to provide a novel apparatus arrangement which permits more eflicient results and provides a reduction in costs of operation and expense of more expensive materials. Another object is to provide an apparatus of the class indicated wherein there is provided a special cracking coil arrangement. Other objects will apear hereinafter. 7

As pointed out above and as may be noted by reference to the patents referred to or other publications, the cracking of ketenizable materials has plished in two chamber or three chamber furnaces. Expressed in another way, there has been employed in certain instances two coils and a crucible or three coils.

In general it isknown from past experience that some increase in efficiency may be accomplished by increasing the size of the furnace from a two chamber to a three chamber construction. This is usually attained to some extent because of better heat utilization and for similar reasons. Accordingly, it was expected that some improvement should be secured by advancing from a three coil process and apparatus to a four coil or chamber setup. However, such four chamber unit, when constructed and piped in a manner generally comparable to the best performing three chamber furnaces, did not give an efiiciency of operation to the degree which seemed desirable. While such four chamber units piped in accordance with prior frequently been accom- 3,136,811 Patented June 9, 1964 constructions were entirely operative and produced good products in substantial yields, the increase in production was only of the order of that attributable to the added chamber.

After extended investigation wefound that if a four coil or chamber furnace was modified in certain respects, not only in certain details of construction, but in particular with respect to the piping, that a much higher degree of efficiency could be obtained. Suchincrease'was substantially greater than could be attributed to the addition of the further chamber. In particular we have found that the cracking coil arrangement in a four chamber furnace could be considerably different from the arrangement heretofore used in prior constructions.

In the broader aspects of our invention we have found that in a four chamber furnace that if two cracking coils are in parallel, one in the third chamber and another in the fourth chamber, quite unusual results may be secured. These parallel cracking coils are connected in series with the preheating and superheating coils in chambers 1 and 2 of said four chamber furnace. By this new arrangement of coils and associated parts, we have found that an increase of production of ketene may be secured to the order or" 40% greater than the production of ketene rom a four chamber furnace and operated like a three chamber furnace of the prior art.

A further understanding of our invention may be had from a consideration of the attached drawing forming a part of the present application.

FIG. 1 is a semidiagrammatic side elevation view in section illustrating a four chamber furnace embodying the coil arrangement of the present invention. As will be apparent hereinafter, since many of the details of construction may be the same as presently used construction for such type of furnaces, extended description of FIG. 1 will not be necessary.

' FIG. 2 is a more fully diagrammatic side elevation view in a particular simplified form for illustrating the pipingand coil arrangement in a four chamberfurnace of the present invention. This figure has been presented in particularto illustrate the basic inventive features of the instant invention.

FIG. 3 is a semidiagrammatic side elevation view of an anhydride forming unit such as may be used in conjunction with the furnaces of the present invention. That is, the ketene produced in the furnaces of the present invention may be utilized in the process and apparatus of FIG. 3 for the production of a uniform anhydride product.

Referring now to FIG. 1, it can be noted that many of the parts shown in this figure may be the same or similar to the parts described in companion Patents 2,- 541,471 and 2,784,065 and that the materials of construction may be the same as described in these patents. The furnace is comprised of afurnace housing 1 which would be of suitable ceramic or brick work for enclosing theseveral coils for preventing heat escape and also for bringing the heating medium in close contact with the coils. The interior of this furnace housing is divided into .four chambers 3, 4, 5 and a. Each of these chambers are separated from the other chambers by suitable baflle walls 7, 8, 9 and 10. These ceramic bafile walls may be of any desired construction such as the various constructions disclosed in 2,541,471 and 2,784,065 just referred to. Chamber 6 is provided with an exit 12 whereby the heating gases may'be exhausted to a stack (not shown).

In the construction shown in FIG. 1, the combustion chamber is provided with one or more burners 13. However, supplemental to or in lieu of the combustion chamher, individual burners may be inserted into each of the chambers 3, 4, 5, etc. In such arrangement the burners are preferably positioned to discharge tangentially of the walls and not to impinge directly on the coils in the chamber. Similar remarks apply to burner 14 in that it would be angled so as not to impinge directly on the coils 25 and 26.

In addition to the refractory baffles and the like just referred to, in at least chambers 3 and 4, and if desired, in the other chambers, there would be provided refractory core members such as 16 and 17 which core members are encircled by the cracking coils to be described in detail hereinafter. Extended description of these core members which may be solid or tubular, is unnecessary inasmuch as the construction thereof may be substantially exactly in accordance with the disclosure in companion Patent 2,541,471.

In each of these chambers of the four chamber furnace there are positioned coils and piping through which is fed the ketenizable material to be cracked or pyrolyzed to the ketene. That is, cracking coils 21 and 22 are positioned in chambers 3 and 4. Superheating preheating coils 23, 24, 25 and 26 are positioned in the other two chambers and 6. A further understanding of this coil arrangement and positioning, which is an important part of the present invention, will be had from a consideration of FIG. 2 which will now be described.

In this schematic and simplified view of FIG. 2, it will be observed that there has been provided the areas 31,- 32, 33 and 34 corresponding to the four chambers referred to above. Such areas or chambers have been further identified by the legends appearing on FIG. 2 as cracking chamber, superheating chamber and preheating chamber.

In connection with the cracking chamber it will be noted that in addition there has been designated the capital letters A and B corresponding to stream A and stream B noted on the left of FIG. 2. In the arrangement of the present invention the piping and coil construction is such that two streams, namely A and B of the ketenizable material may be fed through the four chamber furnace simultaneously, the two streams joining at point 35 to leave the furnace through the single conduit 36.

An important feature of the piping and coil arrangement of the present invention is that chambers 31 and 32 each contain a cracking coil 38 and 39 piped in parallel.

Considering cracking coil 38, this is connected by conduit 41 to the superheat coil 42, which superheat coil is connected by conduit 43 to the preheat coil 44. This preheat coil leads back through conduit 45 to the feed (stream A) of the ketenizable material.

In a similar manner, cracking coil 39 is connected by a conduit 46 to a superheating coil 47. It will be noted that this superheating coil 47 is positioned below coil 42 of line A. However, the particular coil that is above or below the other coil is not an undue limitation on the present invention. In general, it is preferred that if the coil of line A is at the top of the superheat chamber, then the coil of the same line would be at the bottom of the preheat chamber inasmuch as such arrangement provides for better heat distribution.

Continuing further with the piping of stream B, it will be observed that the superheat coil 47 is connected by conduit 48 to the preheat coil 49 which coil leads into the feed of stream B through conduit 50.

From this simplified piping diagram it will be observed that two streams A and B of ketenizable material may be fed into the four chamber furnace of the present invention. In each instance each stream A and B is subjected to approximately comparable preheating and superheating treatment in the chambers 34 and 33. Then each of the streams A and B enters its separate cracking chamber 32 and 31 wherein the final pyrolysis takes place. The resultant pyrolysis products are united at point 35 to the single conduit 36 through which the pyrolysis products are conducted to a condenser and other treatments to separate and/ or utilize the products.

We have discovered that the capacity of the furnaces of the class under description is limited both by pressure drop in the tubing and by heat input to the furnace. We have found that the new arrangement of the present invention providing two cracking coils in parallel and otherwise in accordance with the arrangement of FIG. 2 has reduced the pressure drop for a given flow rate and allowed an increase in feed of 40%. Expressed in another way, by the new piping arrangement of the present invention the pressure drop obtained is equivalent to the pressure drop obtained in a conventional three coil furnace.

Referring now to FIG. 3, we have disclosed process and apparatus by which the ketene produced by the present invention may be utilized. The ketene leaving the furnace through conduit 36 may be passed into a condenser 60, the condensables are withdrawn at 61. The ketene gas thus preliminarily treated passes through conduit 62 into scrubber 63. In this scrubber the ketene gas is contacted with a circulating stream of a mixture of acetic anhydride and acetic acid entering the scrubber through conduit 64.

Acetic acid is admitted to this scrubber system through the supply line 65 which supply line contains therein automatic valve 66. The reaction product of the ketene with the acetic acid Withdrawn from the bottom of the scrubber at point 67 is pumped by pump 68 through heat exchanger 6% and then through the orifice device 70. This device is associated with the control system 71 which is interconnected with valve 66 aforementioned. The reaction product overflows from scrubber 63 through conduit 74.

The control device functions to automatically measure the specific gravity of the flowing stream which is bypassed through lines 72 and 73. Such measurements are based on the specific gravity and the operation of valve 66 in response thereto permits the automatic control of the reaction product of the ketene with the acetic acid to an accuracy within O.3%. This permits the utilization of the ketene for making a more uniform acetic anhydride.

A still further understanding of our invention will be had from a consideration of the following examples which are set forth to illustrate certain of our preferred embodiments of operation.

Example I In accordance with this example a comparison is made between operation in accordance with the present invention and operation by the older (prior art) procedure.

Old procedure (1) New procedure (2) Same as in old.

According to operation in accordance with the new procedure of the present invention, each of the first two coils is divided into two separate halves and each of the two parallel flow paths passes through /2 in each furnace chamber as shown in FIG. 2. Preferably in order to equalize the heat transfers in the two paths, one path traverses the half-coil in the hotter end of one chamber (i.e., the end at which the hot gases enter) and through the half-coil in the cooler end of the next chamber. As indicated above, there is little preference as to which chamber is reversed in this regard with respect to the other.

To supply additional heat for the increased capacity obtained by the present invention, auxiliary gas-fired burners are used in the first chamber, now known as the preheat chamber. The use of burners in such chamber increases the temperature of the fiue gas leaving the furnace. As already indicated above, when burners are inserted in the chambers, they are preferably positioned so the flame will not impinge directly on the coils. The fuel gas usage as indicated was 2.25 cu. ft. per lb. of anhydride on procedure 1) and is 2.5 cu. ft. per lb. of anhydride on procedure (2). In addition to the 40% increase in production, an 11% increase in gas usage per pound of anhydride produced was incurred.

In further detail asmay be noted by reference to FIG. 2 stream A and.'stream B flow in parallel through the preheat chamber, superheat chamber and then stream A goes to the fourth chamber designated the A cracking chamber and stream B goes to the third chamber designated B cracking chamber. Stream A goes to the bottom half of the preheat chamber and to the top half of the superheat chamber while stream B goes to the top of the preheat chamber and to the bottom of the superheat chamber.

The hot combustion gases from the A cracking chamber leave this chamber at the bottom and enter the B cracking chamber at the bottom and leave at the top thereof. The waste gases leave the superheat chamber at the bottom andenter the preheat chamber. The preheat chamber coils have a shell inside the coil. The hot gases entering at the bottom of the preheat chamber travel upward around the coils and outside-the shell and enter the shell at the top of the chamber and travel down past the draft damper on to the steam generator and the waste gas stack. r g

In the present example, gas burners are fired in the annular space around the coil in the preheat chamber supplying additional heat. As indicated in the above table, in the pyrolysis of acetic acid as streams A and B and the conversion thereof to acetic anhydride the present invention gave about a 40% increase of anhydride.

Example 11 In accordance with this example an apparatus in accordance with FIG. 1 and having the coil arrangement of FIG. 2 was employed for carrying out the conversion of acetic acid to ketene. Feeds A and B were comprised of glacial acetic acid of approximately 99.95% purity. The acetic acid, as it entered the preheat chamber of FIG. 2, had injected therein a small amount of catalyst. That is, there was incorporated in the acetic acid feed a small amount of a 'tri-lower alkyl phosphate catalyst. Suitable catalysts aretrimethyl phosyphate, tri-isopropyl phosphate and tripropyl phosphate and other phosphate esters of this type. Streams A and B which are in series in the preheat and superheat chambers were subject to a temperature in the preheat chamber within the range of 700-800 C. In the superheat chamber the temperature range was within the range of 9001l00 C.

In the cracking chambers where the coils are in parallel arrangement, the temperature Was within the range of 9001100 C. The heat was supplied by several burners positioned in all the chambers as needed to supply sufficient heat by burning natural gas to maintain the temperatures specified aforesaid in the respective chambers.

The pressure drop with the piping and coil arrangement of the present invention, from the point of entry before the feed of the preheat zone to the exit at conduit 36 was of the order of 240 mm. As may be noted, such pressure drop is relatively low and compares favorably with the pressure drop of two and three chamber furnaces.

The rate of feed of the glacial acetic acid to the process in each separate line in accordance with this example was of the order of 2700 lbs. per hour. The conversion of such feed to ketene was of the order of 80-85%.

The ketene produced in accordance with this example was reacted with acetic acid in an apparatus as diagrammatically disclosed in FIG. 3 to give a high quality uniform acetic anhydride. As described above in connection with FIG. 3, the reaction of the ketene and acetic acid is controlled by continuously withdrawing a controlled reaction wherein the feed of the acetic acid reacted with the ketene is controlled by the specific gravity of the reaction product, there was obtained a very uniform acetic anhydride.

Expressed in another way, operating in accordance with the present example wherein the pyrolysis was accompli'shed in a four chamber furnace with the two cracking coils in parallel, there was obtained 91,000 lbs.- per day of relatively uniform acetic anhydride. This represents approximately a 26,000 lbs. per day increase of production over a four chamber furnace which was piped and otherwise operated in accordance with prior art procedures.

The following further examples are set forth to illustrate difierent feed rates, different temperature ranges of the preheat, superheat and cracking zones and the like variations in our process. However, apparatus as described above in detail was used. Y

Example III With the temperature of the acid stream leaving the cracking chamber 740 C. and a feed rate of 2700 pounds of acid per hour, a production rate of 88,000 pounds per day of acetic anhydride was obtained.

Example IV With the temperature of the acid stream leaving the cracking chamber at 730 C. and a feed rate of 2700 pounds of acid per hour, a production rate of 86,000 pounds per day of acetic anhydride was produced.

Example V With an acid stream temperature leaving the cracking coil at 740 C. and a feed rate of 2900 pounds of acetic acid per hour, a production rate of 89,000 pounds of acetic anhydride was produced per day.

Example VI With the temperature of the acid stream leaving the cracking chamber at 730 C. and a feed rate of 2900 pounds per hour, a production rate of 88,000 pounds of acetic anhydride per day was obtained.

Example VII In operating the furnace as per the conditions shown in Example II but using acetone as a feed, a conversion of is obtained with a production of 90,000 pounds of acetic anhydride while feeding 62,000 pounds of acetone.

In the above examples the furnace construction, interior partition walls and the like were of refractory material such as high temperature fire bricks. The piping and coils were constructed of chromium steel containing refractory encircled by the coils as described in the abovementioned Patent 2,541,471. In general we prefer to construct the coils and piping of a chromium-aluminum steel or chromium-nitrogen steel as shown in US. Patent 2,393,778. However, certain stainless steel as Type 446 may be used. Also Types 405, 406, 430 and 440 may be used in some instances when necessary.

Although the process has been described primarily with respect to the conversion of acetic acid to ketene, this being one of the principal types of conversions carried out commercially, our process and apparatus may be utilized in the pyrolysis of other ketenizable materials exemplified by acetone, ethyl acetate, propionic acid and other ketones and acids of this type.

It is thought apparent from the foregoing that we have provided a new and improved piping and coil arrangement which is specially adapted for four chamber furnaces for the production of ketene from the pyrolysis of acetic 7 acid whereby increased production capacity may be obtained from the apparatus without increased floor space or the use of larger quantities of the heat resistant chromium containing steel used to prepare coils. Also, we have shown that the ketene produced may be readily converted to a relatively uniform acetic anhydride.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A process for the production of ketene which c0mprises directing separate streams of acetic acid containing a small amount of a tri-lower-alkyl phosphate catalyst into a single preheating zone, the first of said separate streams being conducted into the upper portion of said zone and circulated therethrough in a spiral course and the second of said separate streams being conducted into the lower portion of said zone and circulated therethrough in a spiral course, thereafter directing the separate streams of preheated acetic acid from said zone next into a second single zone wherein said streams are heated to a some what higher superheating temperature, the stream coming from the lower portion of said first zone being conducted into the upper portion of said second zone and circulated therethrough in a spiral course and the stream coming from the upper portion of said first zone being conducted into the lower portion of said second zone and circulated therethrough in a spiral course, then directing the separate streams of superheated acetic acid to two separate pyrolysis zones situated in parallel, circulating said streams through said separate pyrolysis zones in separate spiral courses thereby cracking the acetic acid into ketene, and joining the separate streams of ketene leaving said separate pyrolysis zones in a single stream of ketene product.

2. The process according to claim 1 wherein the temperature of the first zone is maintained at about 700800 C. and the temperature of the second zone and the pyrolysis zones at about 9001100 C.

3. The process according to claim 1 wherein the single stream of ketene product is treated with acetic acid to produce acetic anhydride, the amount of acetic acid being automatically controlled in response to the specific gravity of a sample stream of acetic anhydride continuously withdrawn.

References Cited in the file of this patent UNITED STATES PATENTS 2,541,471 Hull et al Feb. 13, 1951 2,743,296 Painter et al Apr. 24, 1956 2,776,192 Painter et al. Jan. 1, 1957 2,784,056 Painter Mar. 5, 1957 2,806,064 McKlveen Sept. 10, 1957 2,863,922 Sturzenegger Dec. 9, 1958 

1. A PROCESS FOR THE PRODUCTION OF KETENE WHICH COMPRISES DIRECTING SEPARATE STREAMS OF ACETIC ACID CONTAINING A SMALL AMOUNT OF A TRI-LOWER-ALKYL PHOSPHATE CATALYST INTO A SINGLE PRHEATING ZONE, THE FIRST OF SAID SEPARATE STREAMS BEING CONDUCTED INTO THE UPPER PORTION OF SAID ZONE AND CIRCULATED THERETHROUGH IN A SPIRAL COURSE AND THE SECOND OF SAID SEPARATE STREAMS BEING CONDUCTED INTO THE LOWER PORTION OF SAID ZONE AND CIRCULATED THERETHROUGH IN A SPIRAL COURSE, THEREAFTER DIRECTING THE SEPARATED STEAMS OF PREHEATED ACETIC ACID FROM SAID ZONE NEXT INTO A SECOND SINGLE ZONE WHEREIN SAID STREAMS ARE HEATED TO A SOMEWHAT HIGHER SUPERHEATING TEMPERATURE, THE STREAM COMING FROM THE LOWER PORTION OF SAID FIRST ZONE BEING CONDUCTED INTO THE UPPER PORTION OF SAID SECOND ZONE AND CIRCULATED THERETHROUGH IN A SPIRAL COURSE AND THE STREAM COMING FROM THE UPPER PORTION OF SAID FIRST ZONE BEING CONDUCTED INTO THE LOWER PORTION OF SAID SECOND ZONE AND CIRCULATED THERETHROUGH IN A SPIRAL CORSE, THEN DIRECTING THE SEPARATE STREAMS OF SUPERHEATED ACETIC ACID TO TWO SEPARATE PYROLYSIS ZONES SITUATED IN PARALLEL, CIRCULATING SAID STREAMS THROUGH SAID SEPARATE PYROLYSIS ZONES IN SEPARATE SPIRAL COURSES THEREEBY CRACKING THE ACETIC ACID INTO KETENE, AND JOINING THE SEPARATE STREAMS OF KETENE LEAVING SAID SEPARATE PYROLYSIS ZONES IN A SINGLE STREAM OF KETENE PRODUCT.
 3. THE PROCESS ACCORDING TO CLAIM 1 WHEREIN THE SINGLE STREAM OF KETENE PRODUCT IS TREATED WITH ACETIC ACID TO PRODUCE ACETIC ANHYDRIDE, THE AMOUNT OF ACETIC ACID BEING AUTOMATICALLY CONTROLLED IN RESPONSE TO THE SPECIFIC GRAVITY OF A SAMPLE STREAM OF ACETIC ANHYDRIDE CONTINUOUSLY WITHDRAWN. 